This invention relates generally to a video source which drives a video receiver with a signal transmitted over a transmission cable, and more particularly the invention is directed to adapting the video source output to match the receiver load.
Video signal sources typically drive a video receiver through a cable transmission line. During normal operation the video output is designed to have two termination resistors, one locally at the source and one at the receiver end of the cable, in order to prevent signal reflections in the cable. However, if only one of the two termination resistors are present, the video source output can double in voltage which results in output signal clipping.
The present invention is directed to adapting the video source output to match a variable load.
In accordance with the present invention a video source is connected to a video receiver through a cable transmission line with the transmission line having one or more load resistors associated therewith. A level detector is provided to detect the output signal from the video source and control the input to the video source as necessary to maintain a desired level for the output signal.
In a preferred embodiment, the video source comprises a current digital to analog converter (DAC), and the level detector comprises a pair of comparators which compare the DAC output to two voltage levels and control a scaler for the input signal to the DAC as necessary to maintain a desired voltage level. Accordingly, if the load impedance increases and the video output increases, the video to the DAC can be reduced. Conversely, if the load impedance decreases and signal output decreases in value, the input to the DAC can be increased in order to maintain the desired output voltage level.
The invention and objects and features thereof will be more readily apparent from the following detailed description and dependent claims when taken with the drawing.